Many electronic devices, such as radiotelephones, include one or more circuit boards having electronic parts assembled thereto. To competitively manufacture these devices, the parts must be assembled to the board via an assembly process that is quality controlled. One way of achieving quality control of the assembly process includes periodically removing a single board from the process to inspect the alignment of the parts assembled to the board using a video metrology system.
The video system includes a placement table to receive a board designated for inspection, a high magnification camera movably positioned above the table, a downward projecting light source positioned above the table to illuminate the received board, and a processing section coupled to the camera. Upon reception of the board, the camera, responsive to coordinates contained in a board layout stored in the processing section, captures an image of a first part and couples the image to the processing section. The processing section, using gray scale image contrasting, detects differences in gray scale levels representing edges of the first part, edges of board attributes, such as pads upon which the part is seated, and edges of the solder attaching the part to the pad. The processing section determines an alignment of the first part from the detected edges and compares the alignment to a range of prestored alignment values contained in the board layout. When the alignment is not within the range, the processing section indicates that the process is out, or is close to being out, of control and must be adjusted. After inspecting the first part, the video system sequentially proceeds to the remaining parts on the board.
Unfortunately, the number of parts assembled to a circuit board used in, for example, a radiotelephone often exceeds 500 and inspection of each part takes approximately 6 secs. Thus, the inspection of a single board can take on the upwards of 3000 secs. If the assembly process is halted during the inspection, a downtime cost resulting in reduced throughput is incurred. If the assembly process is allowed to continue during the inspection and misaligned parts are found, a sizable cost associated with allocating repair resources to rework each of the circuit boards built during the inspection is incurred.
In addition, each circuit board to be inspected must have a corresponding layout stored in the video system. A separate layout must be stored in the video system for each circuit board having a different topography. For competitive manufacturers that build a variety of different devices having different circuit boards, a sizable cost associated with the creation and maintenance of many board layouts is incurred.
Therefore, what is needed is an apparatus and method that reliably measures the accuracy of highly populated circuit boards without h having to inspect each part assembled thereto and facilitates management of a large number of unique circuit board topographies.